The invention relates to a monitoring device for monitoring the operation of a printer, such as a sheet-fed offset printer.
Sheet-fed offset printers have a number of units, such as the feeder, delivery device, printing groups, coating and processing devices. Different operating elements in the form of control switches are provided to operate these individual units and the printer as a whole, through which machine operation, certain operational functions, etc., can be initiated. The moving elements, such as cylinders and rollers, are protected by protection elements movable for maintenance purposes, in order to prevent the operator from being exposed to danger from a running machine due to an open protection circuit. The protection elements are protected by sensors and switch elements designed as limit switches. The signals of the operating elements in the individual units, as well as the sensors and switches that protect the individual protection systems, are connected to one or more stations, forming the controller of the printer, which are preferably configured as a computer. A controller, which consists of at least one computer and that records the signal states of the different control elements and protective switches, is known from DE 43 27 848 A1 and EP 0 243 728 A2. DE 195 27 089 A1 and 195 20 918 A1 describe the individual units of the stations designed as a computer and connected to the printer, which combine to form the controller of the printer.
As is known from DE 43 27 848 A1 and EP 0 243 728 A2, certain functions of a printer must be protected redundantly, i.e., the activation of a control element or the opening of a protection system causes the immediate shutdown of the corresponding drive, especially the main drive of the printer. As a result, the signals of the corresponding operating element and the switches that protect the protection system are fed both to the controller and, parallel to it, to a monitoring device configured as a computer. Switching of the drive or drives as a function of the signal state then occurs both via the controller and via the monitoring device. Shutdown therefore also occurs during failure of the controller.
The variety of operating elements and safety elements (switches, sensors) results in high cabling expense due to the redundant monitoring of the signal transmitters. The high cable expense also hinders the search for errors during cable defects or malfunctions in the corresponding plug-in connectors.
The large number of operating and protection elements to be monitored (switches, sensors) also causes a high computer load on the monitoring system. This is especially true, since it must be guaranteed by the controller and by the monitoring system that a specific reaction, especially shutdown (stopping) of the printer, occurs within a stipulated interval at specified signal states.
In view of the foregoing, it is an object of the invention to provide an improved monitoring device for a printer, especially a sheet-fed offset printer, that enables easy error identification in the event of a malfunction, while avoiding the aforementioned shortcomings of prior art monitoring devices.
The monitoring device according to the invention has a bus system, via which several computers that enter the signal states of the operating elements, switches and sensors and function as slaves are connected to a master computer. Commands to enter the input (signal state) are repeatedly sent to the individual slaves via the bus system by the master connected to the actual monitoring computer. In response to a command, the individual slaves send an indicator of the inputs present in them (signal states of the operating elements, switches, sensors). The master, connected after the monitoring computer, thus obtains, on each query, an indication of all the input states in the individual units to which the slaves of the monitoring device according to the invention are assigned. The monitoring computer then generates, from its overall input indication, switching commands for the drives and actuators being monitored. If a state results from the input indication entered by the master, based on which a drive or actuator, and especially the main drive of a printer, is to be stopped, this command is sent via the bus system to the corresponding slave in the corresponding unit. The slave receiving this command then causes switching off or stopping of the actuator/drive.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawing, in which: